Abstract:

The intriguing size- and shape dependent properties of nanoparticles have garnered recent attention in many science and engineering areas. When the particle size is in the nanometer size range, the material exhibits very different properties such as surface plasmon resonance (of gold nanoparticles) and superparamagnetism (of iron oxide nanoparticles). The size-dependent properties of quantum dots have made them useful as UV-Vis-NIR sensors and in telecommunications applications. However, the separation and purification of nanoparticles are still challenging due to their size, insolubility in many solvents, and irreversible adsorption to other materials. Membrane filtration is widely used to separate nano-sized biological materials such as proteins, viruses, DNA and RNA. This dissertation presents novel approaches to the use of ultrafiltration and nanofiltration membranes for nanoparticle separation and purification using dead-end and cross-flow filtration techniques.
Purification of phosphine-stabilized Au₁₁ (Au₁₁(PPh₃)₈Cl₃, M.W. 4371, d[subscript core]=0.8 nm), produced in a microreactor without recrystallization, was achieved using nanofiltration membranes. The ceramic and polymer nanofiltration membranes were able to purify the Au₁₁ with rejection values higher than 90%. A novel continuous nanofiltration system design was applied and characterized. The continuous synthesis process, coupled with continuous nanofiltration, resulted in a significant reduction in synthesis time while producing higher yield than could be achieved in batch experiments. The diafiltration system was applied towards isolation of Au₁₁, and results were presented that indicate increased yield and enhanced product purity.
Organic-solvent resistant nanofiltration and ultrafiltration membranes were applied for purification and size-based separation of lead sulfide nanoparticles and gold nanoparticles that were initially synthesized with a 2-8nm size distribution. The nanofiltration membranes achieved rejection values greater than 95% for each of the nanoparticle samples and retained most of the nanoparticles on the membranes. The nanofiltration membranes also exhibited high permeability, which translates to a reduced purification time. Ultrafiltration membranes were screened and successfully applied to the size fractionation of lead sulfide nanoparticles and gold nanoparticles.
A templated silsesquioxane (ssq) membrane was synthesized within the pore space of an alumina support membrane and used for the separation and purification of nano-sized materials such as nanoparticles and macromolecules. The ssq membrane was fabricated by polycondensation of a silsesquioxane monomer solution in the presence of a surfactant within the macroporous space of an Anodisc alumina membrane (Whatman, CO. Ltd, Maidstone, UK). The novel ssq membranes were successfully applied for size exclusion separations of organic soluble 5-8 nm gold nanoparticles (protected with dodecanethiol). A ssq membrane also proved useful for the separation of biological macromolecules such as bovine serum albumin and myoglobin.